Lawnmowers have generally hitherto been designed either to catch lawn clippings in a catcher for disposal, or to recut or mulch clippings and discharge them back into the lawn.
Prior art lawnmower blades, whether disc and flail blades or bar type blades, designed for ejection of the clippings via a discharge chute in the blade housing do not mulch and disperse the clippings satisfactorily back into the cut lawn even when mounted to a lawnmower housing designed for this purpose.
Lawnmower blades designed for mulching and discharge of clippings back into the lawn often fail to operate satisfactorily in wet grass, and also do not satisfactorily perform catching or scattering of clippings, especially if the discharge chute is disposed rearwardly in the blade housing. Various forms of blades have been designed for the purpose of cutting and mulching the grass and dispersing of the clippings back into the lawn, as described in U.S. Pat. Nos. 2,809,488, 3,003,298, 3,382,653, 3,531,923, 4,134,249, 4,292,791) and 4,617,788.
These mulching blades typically produce uplift and/or downdraft, which in conjunction with a suitably shaped blade housing causes a cycling of air and clippings substantially inwards and downwards as the means for dispersing the clippings into the lawn, and do not perform said dispersal satisfactorily when fitted to a lawnmower with restrictions or variations in the height of the blade housing, such as a raised discharge runway.
The prior art includes attempts to achieve dual operations, either discharging clippings into a catcher or alternatively dispersing the same back into the lawn, such as in U.S. Pat. Nos. 3,085,386, 3,132,457 and 3,192,692, which show a mulching assembly with allowance for a discharge opening in the blade housing.
The housing does not include a raised discharge runway to facilitate discharge of the clippings into a catcher, as such a runway would tend to disrupt the aforementioned cyclical airflow and adversely affect the dispersal of the clippings into the lawn when mulching. The discharge opening is positioned on the side, rather than the rear of the blade housing to allow removal of the clippings from within the blade housing as soon as possible.
The catching performance is relatively poor because this type of blade does not produce significant circumferential circulation within the blade housing to effectively eject the clippings out of the blade housing and into a catcher. The inwards and downwards circulation generated by the prior art mulching blades causes a substantial proportion of the grass clippings to be recut before being discharged from the blade housing when catching. This mices moisture and juices from the clippings, which can cause clogging and make emptying the catcher difficult, especially if the grass being cut is wet or lush. An appreciable portion of the clippings also tend to be dispersed into the lawn in the process. The fine mulch does not lend itself to being discharged with sufficient energy to compact well into the catcher.
Furthermore, said prior an bar type blades exhibit a noted tendency towards bending or deforming the engine or blade shaft to which they are attached at times when certain obstructions are encountered, due to the end of the blade being forced downwards as it moves forwards under the obstruction. This is due in pan to the particular configuration of the extreme outer cutting tip.
A further problem encountered with the prior blade mentioned above is the tendency to enwrap certain types of leaves, especially long leaves such as flax, as well as pieces of rope or cord encountered on the lawn around the crankshaft, due to the upwards and inwards flow of air, which tends to carry such material towards the crankshaft.
Mulching blades by and large suffer from a relatively high level of abrasion due to the presence of the cut material, including grit being held in circulation within the blade housing before being dispersed onto the lawn. This extra wear loading affects the outer end, especially the cutting edge as well as the lifting from the trailing edge, necessitating replacement of the entire blade assembly because of wear mainly at these points. The sharp cutting edge of the prior an blade discussed tends to become blunt and deformed when obstructions to the blades travel are met.
The prior an includes a number of embodiments which utilize a fan or perforate disc for producing airflow and/or downdraft, such as those described in U.S. Pat. Nos. 2,737,772, 2,796,714, 2,888,796, 3,110,996, 3,170,276, 3,220,170, 3,905,181 and 4,161,096 in an attempt to address some of the above-mentioned drawbacks. These blade systems are designed to work by and large in conjunction with a particular blade housing configuration, and do not satisfactorily mulch nor necessarily effect satisfactory catching of discharged clippings when affixed to other commonly used lawnmower housings.
A noted drawback with conventional disc and flail blades is the possibility for the flail blade to rotate backwards and strike the body of the disc at times when an obstruction is encountered. This not only tends to damage or deform the flail blade and the disc itself, but may at times result in jamming of the flail blade below the disc body, requiring freeing manually at the expense of safety and convenience.
None of the above systems address the range of disadvantages noted above to a satisfactory degree, nor provide a cutting system which can be transported to a variety of blade housing configurations and maintain satisfactory performance whether catching, scattering or mulching the grass clippings and the like.